The present invention relates to cutting tool insert consisting of a tungsten carbide based hard metal substrate and a coating. The hard metal has an iron-nickel binder phase exhibiting a face centered cubic (fcc) structure. As a result, a coated hard metal insert with no cobalt and at least as good performance in machining as a corresponding coated hard metal insert with Co-based binder has been obtained. The insert is useful in milling and turning of low and medium alloyed steels as well as stainless steels.
In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
Hard metals are composite materials comprising grains of a hard phase and a binder phase that binds the hard phase grains. An example of a hard metal is tungsten carbide (WC) and cobalt (Co), also known as cobalt cemented tungsten carbide or WCxe2x80x94Co. Here, the hard component is WC while the binder phase is cobalt based, for example, a cobalt-tungsten-carbon alloy. The Co content is generally 6-20 wt-%. The binder phase is mainly composed of cobalt in addition to dissolved W and C.
Cobalt is, thus, the major binder in hard metals. For example, about 15 percent of the world""s annual primary cobalt output is used in the manufacture of hard materials including WC-based cemented carbides. About 25 percent of the world""s annual primary cobalt output is used in the manufacture of superalloys developed for advanced aircraft turbine enginesxe2x80x94a factor contributing to cobalt being designated a strategic material. About half of the world""s primary cobalt supply is obtained in politically unstable regions. These factors not only contribute to the high cost of cobalt but also explain its erratic cost fluctuations.
Industrial handling of hard metal raw materials may cause lung disease on inhalation. A study by Moulin et al. (1998) indicates that there exists a relationship between lung cancer and exposure to inhaled particles containing WC and Co.
Therefore, it would be desirable to reduce the amount of cobalt used as binder in hard metals.
Attempts have been made to achieve this goal in hard metals by substituting the Co-based binder phase with an iron rich iron-cobalt-nickel binder phase (Fexe2x80x94Coxe2x80x94Ni-binder). Hard metals with an iron rich Fexe2x80x94Coxe2x80x94Nixe2x80x94binder have thus been strengthened by stabilizing a body centered cubic (bcc) structure in the Fexe2x80x94Coxe2x80x94Nixe2x80x94binder. This bcc structure was achieved by a martensitic transformation. Hard metal with enhanced corrosion resistance has been obtained with a nickel rich nickel-iron binder at high binder contents.
EP-A-1024207 relates to a sintered cemented carbide consisting of 50 to 90 wt-% submicron WC in a hardenable binder phase. The binder phase consists of, in addition to Fe, 10-60 wt-% Co,  less than 10 wt-% Ni, 0.2-0.8 wt-% C and Cr and W and possibly Mo and/or V.
JP 2-15159 A relates to a substrate consisting of a hard phase with composition (Ti,M)CN, where M is one or more of Ta, Nb, W, and Mo. In addition, there is a binder phase selected from the group Co, Ni, and Fe. The substrate is coated with a Ti-based hard coating.
U.S. Pat. No. 4,531,595 discloses an insert for earth boring tools, such as drill bits, with diamonds imbedded in a sintered matrix of WC and a Nixe2x80x94Fe binder. The matrix prior to sintering has a particle size of from about 0.5 to about 10 xcexcm. The Nixe2x80x94Fe binder represents from about 3% to about 20% by weight of the matrix.
U.S. Pat. No. 5,773,735 discloses a cemented tungsten carbide body with a binder phase selected from the group Fe, Ni, and Co. The average WC grain size is at most 0.5 xcexcm and the material is free of grain growth inhibitors.
In U.S. Pat. No. 6,024,776 cemented carbides having a Coxe2x80x94Nixe2x80x94Fexe2x80x94binder are described. The Coxe2x80x94Nixe2x80x94Fexe2x80x94binder is unique in that even when subjected to plastic deformation, the binder substantially maintains its face centered cubic crystal structure and avoids stress and/or strain induced phase transformations.
WO 99/59755 relates to a method for producing metal and alloy powders containing at least one of the metals iron, copper, tin, cobalt, or nickel. According to the method an aqueous solution of metal salts is mixed with an aqueous carboxylic acid solution. The precipitate is then separated from the mother liquor and thereafter reduced to metal.
A cutting tool insert has a tungsten carbide based hard metal substrate and a coating. The hard metal has 4-15 wt. % of a binder phase having a face centered cubic structure. In one embodiment, the binder phase has 35-65 wt. % Fe, minor amounts of W, C, Cr, V, Zr, Hf, Ti, Ta, or Nb, and the balance Ni. In an additional embodiment, the binder phase has 40-60 wt. % Fe, minor amounts of W, C, Cr, V, Zr, Hf, Ti, Ta, or Nb, and the balance Ni. The coating has an inner layer of about 2-4 xcexcm Ti(C,N) and a multilayer of about 2-4 xcexctm Al2O3 and TiN, the multilayer following the inner layer.